Circuit for controlling fluorescent lamps



Nov. 37, 1942.

C. V. AGGERS' CIRCUIT FOR CONTROLLING FLUORESCENT LAMPS Filed March 22 1940 INVENTOR C. 1 9 76586 ATTORNEY Patented Nov. 17, 1942 2,302,285 cmcurr FOR. comonmvc FLUORESCENT LAMPS Clair V. Aggers, Forest Hills,

Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a

Pennsylvania corporation of Application March 22, 1940, Serial No. 325,338 6 Claims. (01. 176-124) My invention relates to a circuit for a discharge device and especially to a starting means for the discharge in a fluorescent lamp.

An object of the invention is to provide amore simplified starting circuit for a discharge device.

Another object is to provide a starting relay for a fluorescent lamp which will provide fast starting at all temperatures and eliminate the possibility of failure of the heater coils at high ambient temperatures.

A still further object of the invention is to have means utilizing the necessary amount of energy for starting the device and then to have the energy demand of this means abruptly decreasing to a minimum for operation.

Other objects and advantages of the invention will be apparent from the following description and drawing, in which- Figure l is a diagrammatic circuit view of the starting circuit for a fluorescent lamp when the current has just been connected to start the lamp.

Figure 2 is a similar view to Figure l illustrating the fluorescent lamp and circuit in operation.

One characteristic of the fluorescent lamp is the time delay necessary for heating up the electrode to provide a cloud of electrons prior to the time the discharge takes place in the lamp. The

efliciency of the fluorescent light, as well as the absence of glare therefrom have enormously increased the utilization of this type of lamp in spite of the more complicated starting circuit and time lag necessary for lighting the lamp over that of the incandescent lamps.

As is well known, the fluorescent lamp has a mercury atmosphere to which may be added noble gases, if desired, for the production of an intense light by the discharge therethrough, and this discharge fluoresces a coating on the wall of the lamp to produce the type of illumination without glare so desirable in store windows and numerous other installations. The electrodes for producing the discharge are coated with strontium, barium and calcium oxide because of the abundant electron supply therein that is released with a minimum of heating energy. The gaseous atmosphere within the tube, however, produces positive ions, and if the discharge is prematurei ly started, the bombardment of these positive ions will knock off portions of this oxide. coating on the electrodes, unless the electrodes have produced a sufiicient flow of electrons to cushion the positive ion bombardment. Accordingly, the 55 fluorescent tubes'are equipped with a starting circuit that delays the discharge through the tube until the electrodes have produced the desirable flow of electrons to cushion the ion bombardment.

One of the difficulties with the prior art has been the fact that, if the starting device was constructed to turn on the device in the shortest time possible, this starting device was too delicate for a long life, and on the other hand, if it was built sturdily for long life, then the device would unduly delay the starting time of the lamp.

It is an object of my invention to provide a starting device for controlling the fluorescent lamp which has a combination of a sturdy, wellconstructed portion capable of withstanding continued long use, and then another portion which shall be utilized only during the short few seconds when the lamp is first connected and yet 7 which will be very sensitive and shorten the time of the starting of the discharge to a minimum.

In particular I propose utilizing a bimetal thermostat in the starting circuit of a fluorescent lamp that will be capable of operating in a short time during cold weather and yet will not burn up during high ambient temperatures.

- A preferred embodiment of my invention is diagrammatically illustrated in Figure 1. A fluorescent tube l0 having its inner walls ll coated with the fluorescent material, such as willamite, has two electrodes I2 and I3 at either end of a long discharge space in the tube. The tube has two exterior connections I 4 and IE to pass current through the electrode [2 and exterior connections I6 and I! for the electrode l3. Connections l8 and I9 extend to any desired source of current. In starting the lamp the electrodes l2 and I3 are first heated by current passing through each of these electrodes in series. The connection between the two electrodes is then interrupted by opening the connection between I5 and H, and an inductive kick from a reactor20starts a discharge through the discharge space inside the tube III to create the illuminating discharge illustrated at 2| in Figure 2. To provide the interruption of the circuit between the two electrodes, I preferably utilize a bi-metallic strip 22 having a bi-metallic contact 23 to make contact at 2l-to a connection 25 to the electrode I2.

Theother end of this electrode l2 has a connection 26 in which a switch 21 is inserted to the connection I9 to the supply circuit. The other end of the bi-metallic strip 28 is connected by 29 to a heating coil 30 surrounding a portion of the bi-metallic strip. This coil is connected in turn by connection 3| to the electrode I3, which is in turn connected by connection 32 to another heating coil 33 surrounding the bi-metallic strip. The other end of this heating coil 33 is connected by connection 34 to the reactor and connection I 8 to the commercial circuit. The bi-metallic strip is accordingly surrounded by two coils 30 and 33, one of which is in series with the connection through the bi-metal to the two electrodes. The other coil 33 is in series between the electrode I3 and the exterior connection I8 to the commercial circuit. The coil 33 can be made of very sturdy construction to supply sufilcient heat to hold the contacts open, but would not have to be designed to rapidly open them. C011 30 could be designed to supply a large amount of heat very quickly. The faster the contacts 23 and 2 1 are opened, the greater is the inductive kick from the reactor 20.

The switch 21 in Figure 1 has just been closed and the current from I8 passes through the reactor 20, coil 33, electrode I3, coil 30, bi-metal 22, electrode I2 and connection I9. The coil 30 heats up the bi-metal very quickly and the bending of the bi-metal in response to this heat opens the contact between 23 and 23, as illustrated in Figure 2. The passage of the current through the bi-metal 22 also adds heating energy to open the contacts. For some applications this heating energy may take the place of that supplied by the coil 30. This opening has been made at the time when the passage of current through the electrodes I2 and I3 has provided suflicient electron emission to cushion the ion bombardment of the discharge. The discharge starts because of the inductive kick ,by the reactor 20.

As soon as the contact between 23 and 24 is broken, the current through the coil 30 is interrupted. In the meantime, however, the coil 33 has heated sufiiciently to maintain the contacts 23 and 24 open. The coil 33, because of its sturdy construction and because it is designed to be continually heated, is capable of very long life, even in high ambient temperatures. The tube will start rapidly during cold weather because of the continued supply of heat from this coil. The coil 30, however, has provided a large amount of heat in a very short time, and having performed the operation of opening the contacts, is allowed to cool.

If the heavy demand of starting was always on quick-heating coil 30, namely by being connected to the current source at all operating times, coil 30 would burn out.

Very little insulation would be required between heater coils 30 and 33 because the maximum voltage between the two coils will be the cathode drop which is approximately four volts.

I have accordingly devised a thermostat arrangement for starting a fluorescent lamp which is very sensitive for quick operation which is essential for this type of starting circuit, and yet one which is capable of standing operation without burn-outs for a long time.

While I have illustrated the electrodes I2 and I3 as directly heated oxide coated electrodes, these electrodes may be of the well-known indirectly heated type with the heater portion connected between I4 and I and I6 and I1 and the oxide coating connected to II and I6 respectively.

It is apparent, of course, that the number and arrangement and shape of the various elements in my preferred embodiment disclosed can be varied and accordingly, I desire only such limitations on my invention as are necessitated by thespirit and scope of the following claims.

I claim:

1. A discharge device having two electrodes therein with a discharge circuit path between said electrodes, 9. bimetal switch connected across said electrodes, and means having heating effect upon and for actuating said bimetal switch, including a coil in series and a coil in parallel with said discharge circuit path between said electrodes, both said coils being in series with said electrodes.

2. A discharge device having two electrodes therein with a discharge circuit path between said electrodes, connections to a source of current from said electrodes, a connection in series through and from one electrode to the other and in parallel to the said discharge circuit path, said last mentioned connection having a bimetal switch element and a heater coil. therefor in series in said connection, and a second heater coil for said bimetal switch in series with the connection between one of the electrodes and the source of current.

3. A discharge device comprising a container having two filamentary electrodes therein and two exterior lead-ins for each of the two electrodes, a connection from one exterior leadin of one electrode to one exterior lead-in of the other electrode, said connection including in series a contact, a bimetal switch adapted to make and break with said contact and a heating foil for said bimetal switch, and connections from the other lead-ins of the electrodes to a source of current, one of said last mentioned connections including a second heating coil for said bimetal switch.

4. A discharge device comprising a container having two widely spaced filamentary electrodes therein, and two exterior lead-ins for each of the two electrodes, a connection from one exterior lead-in of one electrode to one exterior lead-in of the other electrode, said connection including in series a contact, a bimetal switch adapted to make and break with said contact and a heating coil for said bimetal switch, and connections from the other lead-ins of the electrodes to a source of current, one of said last mentioned connections including a second heating coil for said bimetal switch.

5. A discharge device comprising a container having a gaseous medium and two spaced heatable electrodes therein, means for applying heating energy to heat said electrodes and then to start the discharge between the electrodes comprising a bimetal switch connected to the two electrodes and tending to remain closed for the transfer of heating energy from one electrode to the other, means for rapidly heating said bimetal switch to open and thereby both start the discharge between the electrodes and interrupt operation of said rapid heating means, and

heavy duty means for heating the bimetal switch continuously to maintain it in open position during the discharge through said device.

6. A discharge device comprising a container having a gaseous medium and two spaced heatable electrodes therein, means for applying heating energy to heat said electrodes and then to start the discharge between the electrodes comprising a bimetal switch connected to the two electrodes and tending to remain closed for the transfer of heating energy from one electrode to the other, means for rapidly heating said blmetal 7 switch to openand thereby both start the disthrough said device, said rapid heating means being effective to open said switch more quickly than said heavy duty means and said heavy duty means remaining eflective after operation of the 5 rapid heating means is interrupted.

CLAIR v. AGGERS. 

